A high tension three-phase circuit breaker includes three poles (referred to below as "pole 1", "pole 2", and "pole 3") which may be operated separately or simultaneously. Insulation is provided in modern high tension circuit breakers by a gas having high dielectric power; a preferred choice is sulfur hexafluoride (SF.sub.6) at a pressure of a few hectopascals, either pure or mixed with nitrogen. The pressure of the insulating gas within the pole enclosures is an important factor which needs to be taken into consideration when a circuit breaker is to be driven, since it would be dangerous to open a pole if subsequent insulation between its contacts could not be guaranteed, due to a lack of pressure. For convenience, this factor is referred to below as "SF.sub.6 pressure" and, if necessary, it may be specified as "pole 1 SF.sub.6 pressure" or "pole 2 SF.sub.6 pressure" or "pole 3 SF.sub.6 pressure".
Each of the poles of a circuit breaker is controlled via a closing coil and an opening coil. The opening coil is powered via a contact of a protection relay; the closing coil is powered via a contact of a reclosing circuit. In a variant, the opening and closing coils may be subjected to manual orders given either locally or remotely.
Each pole of a circuit breaker is provided with a device for detecting the position of its moving equipment:
a first device known as an "opened auxiliary contact" (referred to below by the initials CAO), provides an electrical signal indicating that the moving equipment has moved from a closed position of the pole to an open position; and PA1 a second device, known as a "closed auxiliary contact" (referred to below by the initials CAF), provides a signal indicating that the moving equipment has moved from an open position of the pole to a closed position.
These auxiliary contacts are preferably of the type described in French patent application No. 91 04 631, of Apr. 16, 1991.
In the above-outlined context of a three pole circuit breaker, the object of the present invention is to provide a control and self-monitoring system for the circuit breaker constituting a basic operating level of an electricity station, also referred to as level zero "0".